The present invention relates to wireless power supplies, and more particularly to inductively powered devices.
The principles of inductive power transfer have been known for many years. As a result of mutual inductance, power is wirelessly transferred from a primary coil (or simply “primary”) in a power supply circuit to a secondary coil (or simply “secondary”) in a secondary circuit. The secondary circuit is electrically coupled with a device, such as a lamp, a motor, a battery charger or any other device powered by electricity. The wireless connection provides a number of advantages over conventional hardwired connections. A wireless connection can reduce the chance of shock and can provide a relatively high level of electrical isolation between the power supply circuit and the secondary circuit. Inductive couplings can also make it easier for a consumer to replace limited-life components. For example, in the context of lighting devices, an inductively powered lamp assembly can be easily replaced without the need to make direct electrical connections. This not only makes the process easier to perform, but also limits the risk of exposure to electric shock.
The use of inductive power transfer has, however, for the most part been limited to niche applications, such as for connections in wet environments. The limited use of inductive power transfer has been largely the result of power transfer efficiency concerns. To improve the efficiency of the inductive coupling, it is conventional to carefully design the configuration and layout of the primary and secondary coils. The primary and the secondary are conventionally disposed within closely mating components with minimal gap between the primary and the secondary. For example, the primary is often disposed within a base defining a central opening and the secondary is often disposed within a cylindrical component that fits closely within the central opening of the base. This and other conventional constructions are design to provide close coaxial and radial alignment between the primary coil and the secondary coil. Several specific examples of patents that reflect the conventional approach of providing a fixed, predetermined physical relationship between the primary and secondary coils include: U.S. Pat. No. 5,264,997 to Hutchisson et al, which discloses an inductive lamp with coaxial and closely interfitting primary and secondary coils; U.S. Pat. No. 5,536,979 to McEachern et al, which discloses an inductive charging device in which the device to be charged is fitted closely within a cradle to position the coils in a fixed, predetermined relationship; U.S. Pat. No. 5,949,155 to Tamura et al, which discloses a shaver with adjacent inductive coils set in a fixed relationship; U.S. Pat. No. 5,952,814 to Van Lerberghe, which discloses an inductive charger for a telephone wherein the physical relationship between the primary and secondary coils is fixed; and U.S. Pat. No. 6,028,413 to Brockman, which discloses a charging device having a mechanical guide for ensuring precise, predetermined alignment between the inductive coils. The conventional practice of providing precise alignment between the primary and secondary coil has placed significant limitation on the overall design and adaptability of inductively powered devices. Further, in conventional inductive systems, the power supply circuit, which drives the primary coil, and the secondary circuit, which inductively receives power from the primary, are designed and carefully tuned to match with one another to maximize the efficiency of the inductive coupling. This too has placed significant limitations on the overall design and adaptability of inductively powered devices.